In modern, multi-track magnetic tape recorders, it is sometimes required to operate one magnetic head in a playback mode while another head operates in the recording mode. For example, such simultaneous operation is required when information stored on one magnetic track is to be read-out processed, and re-recorded on another track. During such simultaneous playback and recording, the magnetic stray fields produce a mutual interaction, commonly called "crosstalk" or crossdubbing, i.e., an interference of the signal, for example, applied to the recording head with the signal being picked up by the head operating in the playback mode. The stray magnetic fields on one of the pickup heads induce a voltage in the other head. For example, the playback signal is adversely affected by voltages induced in the playback head by the stray fields from the recording head.
The general problem of crosstalk in magnetic recording and playback systems is discussed, for example, in "Technik der Magnetspeicher," (Technology of Magnetic Storage Apparatus) 2nd edition, 1977, Springer editions, pages 123 and 124. This publication recommends the use of attenuating shields between the magnetic recording and playback heads for reducing crosstalk. Such methods result in maximum attenuation values of approximately 50 dB which still results in the playback amplifying system to begin to oscillate when the spurious signals from the recording head are played back under amplification.
The German Patent Disclosure Document No. 20 52 179 recommends a physical separation of the two magnetic heads in the direction of motion of the magnetic tape. However this remedy is not compatible with fixed standards, for example the SMPTE-1, type B standard, which applies to video and audio recording. Such standards do not permit the occurrence of time delays between different tracks of the same tape in playback and mixing processes.